The firm is working on a host of jobs including the refurbishment of Buckingham Palace where the Enquirer understands work stopped last week after a worker tested positive for the coronavirus.

Chief executive Paul Hamer said: “Following the Government statement of 23rd March, we, like the rest of the UK, are adhering to government guidance and many of our sites and offices are now closed.

“For the Sir Robert McAlpine family and our entire team this was a very difficult action to take. Our overriding aim is always to keep all our sites open and fully operational. This is to ensure we meet our clients’ needs and are able to provide employment for the thousands of people who keep our business thriving.

“Since the start of the UK coronavirus (COVID 19) outbreak we have worked closely with our clients and project partners to do all we can to keep our people safe and our sites running.

“We introduced numerous measures to safeguard our people, including asking as many colleagues as possible to work from home to stop the spread of COVID-19 and reduce unnecessary travel.

“I am proud to say that, despite the added challenges this has brought, our project teams across the country have risen to the task and have done a fantastic job in incredibly difficult circumstances.

“However, given the most recent developments we do not believe we should be asking our people to travel on public transport.

“We cannot operate canteens on our sites; we are not classified as key workers; and upholding the social distancing rule is unfeasible on some of our projects. Because of this then we are unable to operate all sites safely and effectively whilst remaining in accordance with COVID-19 guidelines.

“We are a values-driven organisation and take our responsibilities as a UK business and community member extremely seriously. We therefore wish to do all we can to prevent the spread of COVID-19 and will be complying fully with the latest government instructions.

“As of Wednesday 25th March 2020, most of our sites will be closed to all but essential safety and security employees. The only sites that remain operational are those where it is absolutely safe to do so and where critical work, such as building hospitals continues, or where we are putting safe shutdown plans into operation.

“While this will have a detrimental impact on progress and impact heavily on our people, we recognise that this action is in the best interests of wider society. It is quite simply the right thing to do.

“Whilst some work has paused our pre-contract work to develop new projects remains on track and continues to be delivered.

“We are sorry for the disruption this will cause to the delivery of our projects. If there was an alternative solution to this problem, we would be taking it and we will keep the situation under constant review.

“Where our people can work from home, depending on childcare and isolation arrangements, they are. We have been incredibly encouraged by the can-do attitude of our people and supply chain and the sterling efforts they continue to make to help keep our business performing during this difficult time.

“Our priority, once it is permitted, is to ensure we are fully operational as quickly as possible and that the damage resulting from the current status is minimised.

“We will be back building Britain’s future heritage as soon as it is safe to do so.”